Mechanisms of Improved Exercise Performance under Hyperoxia

Abstract

Background: The impact of hyperoxia on exercise limitation is still incompletely understood. Objectives: We investigated to which extent breathing hyperoxia enhances the exercise performance of healthy subjects and which physiologic mechanisms are involved. Methods: A total of 32 healthy volunteers (43 ± 15 years, 12 women) performed 4 bicycle exercise tests to exhaustion with ramp and constant-load protocols (at 75% of the maximal workload [W_max] on FiO₂ 0.21) on separate occasions while breathing ambient (FiO₂ 0.21) or oxygen-enriched air (FiO₂ 0.50) in a random, blinded order. Workload, endurance, gas exchange, pulse oximetry (SpO₂), and cerebral (CTO) and quadriceps muscle tissue oxygenation (QMTO) were measured. Results: During the final 15 s of ramp exercising with FiO₂ 0.50, W_max (mean ± SD 270 ± 80 W), SpO₂ (99 ± 1%), and CTO (67 ± 9%) were higher and the Borg CR10 Scale dyspnea score was lower (4.8 ± 2.2) than the corresponding values with FiO₂ 0.21 (W_max 257 ± 76 W, SpO₂ 96 ± 3%, CTO 61 ± 9%, and Borg CR10 Scale dyspnea score 5.7 ± 2.6, p < 0.05, all comparisons). In constant-load exercising with FiO₂ 0.50, endurance was longer than with FiO₂ 0.21 (16 min 22 s ± 7 min 39 s vs. 10 min 47 s ± 5 min 58 s). With FiO₂ 0.50, SpO₂ (99 ± 0%) and QMTO (69 ± 8%) were higher than the corresponding isotime values to end-exercise with FiO₂ 0.21 (SpO₂ 96 ± 4%, QMTO 66 ± 9%), while minute ventilation was lower in hyperoxia (82 ± 18 vs. 93 ± 23 L/min, p < 0.05, all comparisons). Conclusion: In healthy subjects, hyperoxia increased maximal power output and endurance. It improved arterial, cerebral, and muscle tissue oxygenation, while minute ventilation and dyspnea perception were reduced. The findings suggest that hyperoxia enhanced cycling performance through a more efficient pulmonary gas exchange and a greater availability of oxygen to muscles and the brain (cerebral motor and sensory neurons).

Effect of hypoxia and hyperoxia on exercise performance in healthy individuals and in patients with pulmonary hypertension: a systematic review

“…In a systematic review of the literature, we identified four randomized-controlled trials, which included a least eight subjects and provided data on the effect of hyperoxia vs. normoxia air on maximal exercise performance in terms of workload or V O 2 (Table A2). All revealed an increased workload of V O 2 under hyperoxia (20,42,48,68).…”

“…They performed two exhaustive progressive ramp and two constant-load cycle cardiopulmonary exercise tests (CPET), each under FI O 2 0.5 and FI O 2 0.21, according to a randomized, sham-controlled crossover trial (68). We found that breathing oxygen-enriched air increased the maximal power output by 5.3% and endurance time in constant-load CPET at 75% of the V O 2max by 52%.…”

“…Since the end-tidal PCO 2 (PET CO 2 ) was increased in hyperoxia compared with normoxia, these findings are consistent with a reduction in peripheral chemoreceptor sensitivity by hyperoxia with relative reduction in alveolar ventilation and a rise in the alveolar PCO 2 (and, hence, PET CO 2 ) (12). The higher CTO with postponed drop toward endexercise under hyperoxia may suggest a role of the brain in exercise limitation (42,66,68). The higher V O 2 under hyperoxia is not entirely understood, but may be related in part to changes in metabolism, redistribution of blood flow, differences in type and recruited muscle fibers, and in metabolism of nonexercising tissues (47,48,68), Higher blood lactate levels due to increased exercise under hyperoxia seem not to play a role (14).…”

Cardiopulmonary Exercise Testing under Hyperoxia: Is the Haldane-Transformation the Correct Approach?

“…With great interest, I read the study by Ulrich et al [1] who investigated the mechanisms of improved exercise performance under hyperoxia. I completely agree with their main conclusion that in healthy subjects, hyperoxia increases the maximal power output and endurance.…”

“…As the HT mainly influences V O 2 , the data from Ulrich et al [1] also indicate that the increase at elevated FI O 2 seems not to be a real increase in V O 2 , but a result of the transformation: while V O 2 is increased, V CO 2 does not increase, and it even seems to decrease somewhat. In addition, the RER_max is much lower under elevat-…”